Submerged well platform

ABSTRACT

A platform supports off-shore wellhead assemblies below the surface of the water at a depth adequate to eliminate danger from surface vessels or storms. Buoyancy tanks reduce the weight supported by the platform and thereby combine with the reduced weight above the ocean floor to reduce the cost of the platform. A seat is provided on the deck of the platform to receive and seal the lower end of a removable access tube that extends upwardly above the surface of the water to allow work at the wellhead to be performed at atmospheric pressure.

United States Patent Wyllie [54] SUBMERGED WELL PLATFORM Malcolm R. J.Wyllie, Allison Park, Pa.

Gull Research & Development Company, Pittsburgh, Pa.

[22] Filed: May 27, 1970 [21] Appl. No.: 40,924

[72] Inventor:

[73] Assignee:

[52] U.S. Cl ..6l/46, 175/5, 175/9 [51) Int. Cl. ..E02d 27/38, B63b35/44 [58] Field of Search ..61/46.5, 46, 0.5; 175/9, 0.5,

[56] References Cited UNITED STATES PATENTS 3,535,884 10/1970 Chaney.l..6l/46.5 3,355,899 12/1967 Koonce et a1... ....61/46.5 3,412,56411/1968 McClintock ..61/46.5

[ 51 May 30, 1972 3,247,672 4/1966 Johnson ..6 H465 X 3,307,624 3/1967Lubinski 3,556,210 1/1971 Johnson ..6l/46 Primary Examiner-Jacob ShapiroAttorney-Meyer Neishloss, Deane E. Keith and Paul L. Tillson [57]ABSTRACT A platform supports off-shore wellhead assemblies below thesurface of the water at a depth adequate to eliminate danger fromsurface vessels or storms. Buoyancy tanks reduce the weight supported bythe platform and thereby combine with the reduced weight above the oceanfloor to reduce the cost of the platform. A seat is provided on the deckof the platform to receive and seal the lower end of a removable accesstube that extends upwardly above the surface of the water to allow workat the wellhead to be performed at atmospheric pressure.

6 Claims, 5 Drawing Figures Pafiemed may 30, 1972 3,665,72fl

3 Shuts-Shut 1 IN VENTOR.

MALCOLM R. J WVLL /E Patented May 30, 1972 5 Shuts-Sh." 2

26 INVENTOR.

MALCOLM RJJ/VVLL/E Patented May 30, 1972 I 3,665,721

5 Shuts-Shut 5 IN VENTOR.

41416014441 WVLL If SUBMERGED WELL PLATFORM This invention relates tothe production of oil from offshore wells and more particularly to aplatform for supporting the wellhead of offshore wells below the surfaceof water.

Much of the oil now produced is produced from wells located offshore.The wellheads of most of such wells are supported on platforms that arelocated at a distance above the surface of the water such that theplatform will not be subjected to pounding by waves. As the search foroil continues, wells are drilled at continually increasing water depths.The cost of platforms for supporting wellheads above the water surfaceincreases very rapidly with an increase in depth of water.

One method that has been suggested for reducing the cost of platformsfor wells in deep water is to use floating platforms. Such structuresrequire a complicated riser and anchoring system and have not beenwidely used. Moreover, floating platforms are exposed to the samehaaards from storm damage and collision as conventional platforms.

This invention resides in a bottom-supported platform forv wells. Theplatform is located at a distance below the surface of the wateradequate to isolate the platform from wave action and eliminate dangerof a surface vessel colliding with the platform. The platform isprovided with storage tanks and buoyancy tanks with suitable connectionsfor varying the weight of fluid in such tanks to adjust their buoyancyand thereby reduce the load on the platform. A seat encircling wellheadson the platform is adapted to receive a removable access tube thatextends from the platform above the surface of the water and permitswork on the wellheads at atmospheric conditions.

In the drawings:

FIG. 1 is a diagrammatic elevational view, partially in verticalsection, of a platform supporting completed wells and with an accesstube in position to permit work on the wells.

FIG. 2 is a diagrammatic elevational view of the platform of thisinvention during the drilling of a well showing a floating drilling rigin position above the platform.

FIG. 3 is a plan view of the platform with the base for the access tuberemoved.

FIG. 4 is a plan view of the base for the access tube.

FIG. 5 is a fragmentary elevational view, partially in vertical section,of the lower end of the access tube.

Referring to FIG. 1, a platform indicated generally by reference numeralis illustrated having legs 12 driven or washed into the ocean floor.Legs 12 slope outwardly to increase the stability of platform 10.Additional stability may be obtained by means of piling 14 driven intothe ocean floor through brackets 16 secured to legs 12. Suitablecross-bracing 18 is provided to increase the rigidity of the platform.

Beams 20 are supported at the upper end of legs 12 and combine withother vertical and horizontal structural members 22 to support a deck 24and an access tube base plate 26. The deck 24 of platform 10 is locatedat a depth below the surface of the water adequate to avoid wave actionduring storms and to eliminate any danger of being damaged by surfacevessels. It is desirable that the platform be located at a depth atwhich divers can work conveniently. Ordinarily, the platform is locatedat a depth of 50 to 200 feet below the surface of the water, andpreferably is located at a level 100 to 150 feet below the surface. Aplurality of guide sleeves 28 extend through deck 24 and base 'plate 26.Guide sleeves 28 are welded to base plate 26 to prevent entry of waterbetween the guide sleeve and base plate into the space above the baseplate.

Extending upwardly from the upper surface of the access tube base plate26 is a circular channel which forms a seat 30 for the access tube.Seating guides 32 slope upwardly and inwardly from the inner uppersurface of access tube seat 30 to guide the access tube into the seat 30as the access tube is lowered onto the platform. Reinforcing webs 34 arelocated at intervals around the access tube seat 30 to provide supportfor the outer wall of the access tube seat 30. Access tube base plate 26has holes extending through it in position to match the holes in thedeck 24 to receive the guide sleeves 28.

Supported on the platform 10 by beams 20 are a plurality of tanks. Inthe arrangement shown in FIG. 3 of'the drawings, the

outermost tanks 36 are used as storage tanks and the inner tanks 38serve as buoyancy tanks.- Since the oil stored in the tanks is lessdense than sea water, the storage tanks provide a buoyant forcecontributing to the buoyant effect of the tanks 38. While the storagetanks have a buoyant effect, it is important to have buoyancy tanks thatat no time will be filled with sea water to maintain at all times abuoyant effect reducing the load on the platform.

Storage tanks 36 are provided with valved oil outlets 40 and the storagetanks 36 and buoyancy tanks 38 have valved air outlets 42 that extendupwardly through the deck 24 to permit connection by divers to lines tothe surface. Lines 41 and 43 above the surface of the deck 24 provideinterconnection between the tanks. In some instances, it may bedesirable to have lines to the surface permanently attached to theoutlets 40 and 42 and supported at the surface by a buoy. Tanks 36 arealso provided with air outlets 44 that are connected by lines 46, thatextend below the deck 24 and rise through the deck 24 and the base plate26, to suitable air connections 48 within the space bounded by theaccess tube seat 30. Similarly, oil outlets 50 are connected by deliverylines 52 below the deck 24 to suitable fittings 54 above the base plate26 within the area bounded by the access tube seat 30. A normally openoutlet 56 is provided in the bottom of the storage tanks 36 to permitflow of sea water into or from the tank as the amount of oil in the tankchanges. Tanks 38 have similar outlets.

Access tube 58 is bell shaped at its lower end to fit the access tubeseat 30. The larger lower end of the access tube extends upwardly adistance adequate to provide sufficient head room for working on wellsenclosed within the lower end of the access tube. The lower end of theaccess tube may have a diameter of the order of 25 to 30 feet. The upperportion of the access tube 58 is of reduced diameter of approximately 6to 10 feet to provide sufficient space for passing men and equipmentnecessary to perform service work on the wells. Access tube 58 has alength adequate to place the upper end 60 of the access tube highenoughabove the surface of the water to prevent water splashing into theopen access tube. It is contemplated that the access tube 58 will havean inner wall 62 spaced from an outer wall 68 and the intervening spacefilled with concrete. Concrete 6 inches thick will provide a structureof sufficient rigidity even though the platform is as much as 300 feetbelow the surface of the water. The lower end of the access tube has asteel base 70 to the bottom of which is secured a deformable sealingelement 72 of rubber or similar material. A steel shoe 74 is secured tothe lower surface of sealing element 72 and bears against the uppersurface of the base plate 26 within the access tube seat 30. The weightof the access tube deforms sealing element 72 against the walls of theseat 30 to prevent flow of water around the lower end of the access tubeinto the space within the access tube.

Access tube 58 is provided with an escape hatch 76 which allows entryinto an escape chamber 78 mounted on the outer surface of the accesstube. The escape chamber is provided with a suitable exit 79 andself-contained breathing apparatus to allow a man to leave the chamberand go to the water surface without having to go through the accesstube.

The platform of this invention will preferably be built onshore,transported to the site on a barge and lowered into position by aderrick. It is preferred that the storage tubes 36 and buoyancy tubes 38have pointed ends 80, and the pointed ends extend in the direction offlow of the currents to reduce the forces exerted on the platform bycurrents below the surface of the water. The weight of the platform canbe adjusted by control of the amount of water in the storage tanks.Water is jetted from the bottom of the legs 12 to lower the legs intothe ocean floor. The platform can be maintained in an upright positionwhile being secured to the ocean floor by selectively jetting water fromthe different legs of the platform. After the legs have been jetted thedesired depth into the ocean floor, a cement slurry is preferably pumpeddown the legs and forced upwardly around the legs to anchor theplatform. Other methods of securing the platform to the ocean floor canbe used. For example, piling can be driven down through the legs 12 ofthe platform or can be driven through brackets 16 secured to the legs.

A drilling rig is moved into place over the platform. In FIG. 2 of thedrawings, a floating drilling rig 82 is illustrated in position over thewell. If the water depth at the well site is not too great, a jack-uprig can be used. Conductor pipe is run through the guide sleeves 28 andeither washed or driven to the desired depth in the ocean floor. Theconductor pipe is then welded to the guide sleeves 28 to prevent flow ofwater upwardly between the guide sleeves and the conductor pipe. Thewell is then drilled and completed by conventional techniques. In theembodiment of the invention illustrated in the drawings, guide sleevesare provided for five wells having wellheads indicated by referencenumeral 84, but obviously any reasonable number of wells can be drilledthrough a single platform. Because of the relatively low cost of theplatform made possible by this invention, it is possible to use moreplatforms with a small number of wells supported by each platform togive greater flexibility in well spacing.

Flow lines 86 from the wells are connected to the storage tanks fordelivery of oil from the wells into the storage tanks, and the outletsat the bottom of the storage tanks opened to permit displacement ofwater from the storage tanks by the oil produced in wells 84. Oil can bedelivered from the storage tanks to a barge for transport to shore by adiver making connections from a barge to outlets 40. The differential inthe density of sea water and oil will allow the sea water to displacethe oil upwardly into the barge.

If the well should need workover, or access to the top of the well isdesired for any reason, the access tube 58 is transported to the site ofthe well and lowered into position with the shoe 74 in the access tubeseat 30. It is contemplated that the ends of the access tube will becovered and the access tube floated to a location above the platform 10.The cover from the lower end of the access tube is then removed. Thelower end of the access tube sinks until the access tube is in anupright position, and air is allowed to escape at a controlled ratethrough the cover on the upper end of the access tube to lower theaccess tube onto seat 30. Placement of the access tube on the seat 30can be facilitated by a float 87 secured to the upper end of the accesstube. After the access tube is directly above the seat 30, air isdischarged from the float 82 to lower the access tube.

Before removing the cover 60 from the upper end of the access tube 58 toplace the full weight of the access tube on the platform, it may bedesirable to reduce the load on the platform to allow for the weight ofthe access tube. That can be accomplished by adjusting the buoyancy bydisplacing water from the storage and buoyancy tanks. Air can bedelivered from a line through outlet 42 into the buoyancy tanks or insome instances into the storage tanks for such displacement. The cover60 is then removed and water pumped from within the access tube. Thebell shape of the access tube results in a large net downward force onthe access tube by the difference in pressure inside and outside of thetube. That force eliminates the necessity of lock-down means to hold theaccess tube in place and improves the seal against the access tube seat.If desired, delivery of oil from the storage tanks can be accomplishedthrough a line extending down the access tube and connected to fittings54. workmen are lowered through the access tube to perform the desiredwork on the wells. When the work on the wells has been completed and theworkmen have left the access tube, the cap 60 is replaced and compressedair injected into the access tube and into the float 86 to lift theaccess tube from the seat 30.

The platform of this invention reduces the danger of damage to theplatform and wells supported by the platform from storm or collisionwith vessels by locating the platform 50 feet or more below the surfaceof the water. The reduction in the height of the platform and thereduced stresses to which the platform is exposed because of itslocation contribute to an important reduction in the cost of theplatform. The buoyancy tanks on the platfonn reduce the load placed onthe platform and further reduce the cost of the structure. Because ofthe reduced costs of the platform of this invention, the use of moreplatforms with improved well spacing becomes economically feasible.

1 claim:

1. A platform for supporting wellheads of offshore wells at a depth of50 200 feet below the surface of the water comprising a plurality ofsubstantially vertical rigid legs extending into and supported by theocean floor, a deck mounted on the upper end of the legs, the length ofthe legs locating the deck at a depth of 50 200 feet below the surfaceof the water, buoyancy tanks connected to and supported by the upperends of the legs to reduce the weight on the legs, oil storage tanksmounted on the upper end of the legs, an upwardly opening access tubeseat on the upper surface of the deck surrounding a plurality ofwellheads supported above the deck by the platform and adapted toremovably receive an access tube of a length to extend above the surfaceof the water, flow lines from the wellheads to the storage tanks, oilfittings above the deck within the access tube seat, oil delivery linesextending from the storage tanks to the oil fittings, air lines openinginto the upper portions of the buoyancy tanks, and openings in the lowerportions of the storage and buoyancy tanks to permit displacement ofliquid from the tanks into the surrounding water.

2. A platform as set forth in claim 1 including oil outlets from thestorage tanks opening above the deck outside of the access tube seat andair connections above the deck outside of the access tube seat openinginto each of the storage and buoyancy tanks.

3. A platform for supporting wellheads of offshore wells comprising legssupported by the ocean floor, a deck mounted on the upper end of thelegs, buoyancy tanks connected to the upper end of the legs to reducethe weight on the legs, the length of the legs placing the deck belowthe surface of the water 50 200 feet, oil storage tanks supported by theupper end of the legs, an access tube base plate on the deck, an accesstube seat on the base plate comprising an upwardly opening channel ofcircular plan surrounding the wellheads supported by the platform andguide surfaces sloping upwardly and inwardly from the inner edge of thechannel, flow lines from the wellheads to the storage tanks, oilfittings above the base plate within the access tube seat, and oildelivery lines extending from the storage tanks to the oil fittings.

4. A platform supporting the wellheads of offshore wells below thesurface of water comprising rigid legs extending downwardly into theocean floor to support the platform with its upper surface at a depth of50 200 feet below the water surface, oil storage tanks supported by thelegs at their upper end, buoyancy tanks supported by the legs at theirupper end, a deck supported by the legs above the level of the tanks andsupporting the wellheads, an access tube seat supported by the deck andsurrounding the wellheads, an access tube constructed and arranged toseat releasably in the access tube seat and seal its lower end, saidaccess tube having a length such that it extends above the surface ofthe water when seated on the access tube seat, means for guiding thelower end of the access tube into the access tube seat, the lower end ofthe access tube having an enlarged diameter to increase the forceexerted by hydraulic pressure urging the access tube against the seatwhen water is removed from the access tube, and means for controllingthe buoyancy of the buoyancy tanks.

5. A platform supporting the wellheads of offshore wells below thesurface of water comprising legs extending downwardly into the oceanfloor to support the platform at a depth of 50 200 feet below thesurface of the water, oil storage tanks supported at the upper end ofthe legs, buoyancy tanks supported at the upper ends of the legs, a decksupported by the legs above the level of the tanks and supporting thewellheads, an access tube seat comprising an upwardly opening channel onthe upper surface of the deck surrounding the wellheads, an access tuberemovably seated in the access tube seat and extending upwardly abovethe surface of the water, a ring of deformable material at the lower endof the access tube adapted to be deformed against the walls of thechannel by the weight of the access tube to seal the lower end of theaccess tube, the lower end of the access tube having an enlargeddiameter to increase the force exerted by hydraulic pressure urging theaccess tube against the platform.

6. A platform for supporting wellheads of offshore wells below thesurface of water comprising a plurality of platform legs engaging theocean floor and extending upwardly therefrom to a level in the range of50 to 200 feet below the surface of the water, buoyancy tanks secured tothe platform legs at the upper end thereof, oil storage tanks supportedby the legs at the upper ends thereof, a deck supported above the tanksby the platform legs, an access tube base plate supported by the deck, aplurality of guide tubes extending downwardly through the access tubebase plate and the deck, wellhead structures connected to casingextending through the guide tube, an access tube seat on the access tubebase plate encircling the wellhead structures and opening upwardly toreceive an access tube, oil lines extending from above the access tubebase plate within the access tube seat to the oil storage tanks, airlines extending from within the access tube seat above the access tubeplate to the buoyancy tanks, and outlets in the lower portion of thestorage tanks and buoyancy tanks to permit the flow of water into andfrom such tanks.

1. A platform for supporting wellheads of offshore wells at a depth of50 - 200 feet below the surface of the water comprising a plurality ofsubstantially vertical rigid legs extending into and supported by theocean floor, a deck mounted on the upper end of the legs, the length ofthe legs locating the deck at a depth of 50 - 200 feet below the surfaceof the water, buoyancy tanks connected to and supported by the upperends of the legs to reduce the weight on the legs, oil storage tanksmounted on the upper end of the legs, an upwardly opening access tubeseat on the upper surface of the deck surrounding a plurality ofwellheads supported above the deck by the platform and adapted toremovably receive an access tube of a length to extend above the surfaceof the water, flow lines from the wellheads to the storage tanks, oilfittings above the deck within the access tube seat, oil delivery linesextending from the storage tanks to the oil fittings, air lines openinginto the upper portions of the buoyancy tanks, and openings in the lowerportions of the storage and buoyancy tanks to permit displacement ofliquid from the tanks into the surrounding water.
 2. A platform as setforth in claim 1 including oil outlets from the storage tanks openingabove the deck outside of the access tube seat and air connections aboVethe deck outside of the access tube seat opening into each of thestorage and buoyancy tanks.
 3. A platform for supporting wellheads ofoffshore wells comprising legs supported by the ocean floor, a deckmounted on the upper end of the legs, buoyancy tanks connected to theupper end of the legs to reduce the weight on the legs, the length ofthe legs placing the deck below the surface of the water 50 - 200 feet,oil storage tanks supported by the upper end of the legs, an access tubebase plate on the deck, an access tube seat on the base plate comprisingan upwardly opening channel of circular plan surrounding the wellheadssupported by the platform and guide surfaces sloping upwardly andinwardly from the inner edge of the channel, flow lines from thewellheads to the storage tanks, oil fittings above the base plate withinthe access tube seat, and oil delivery lines extending from the storagetanks to the oil fittings.
 4. A platform supporting the wellheads ofoffshore wells below the surface of water comprising rigid legsextending downwardly into the ocean floor to support the platform withits upper surface at a depth of 50 - 200 feet below the water surface,oil storage tanks supported by the legs at their upper end, buoyancytanks supported by the legs at their upper end, a deck supported by thelegs above the level of the tanks and supporting the wellheads, anaccess tube seat supported by the deck and surrounding the wellheads, anaccess tube constructed and arranged to seat releasably in the accesstube seat and seal its lower end, said access tube having a length suchthat it extends above the surface of the water when seated on the accesstube seat, means for guiding the lower end of the access tube into theaccess tube seat, the lower end of the access tube having an enlargeddiameter to increase the force exerted by hydraulic pressure urging theaccess tube against the seat when water is removed from the access tube,and means for controlling the buoyancy of the buoyancy tanks.
 5. Aplatform supporting the wellheads of offshore wells below the surface ofwater comprising legs extending downwardly into the ocean floor tosupport the platform at a depth of 50 - 200 feet below the surface ofthe water, oil storage tanks supported at the upper end of the legs,buoyancy tanks supported at the upper ends of the legs, a deck supportedby the legs above the level of the tanks and supporting the wellheads,an access tube seat comprising an upwardly opening channel on the uppersurface of the deck surrounding the wellheads, an access tube removablyseated in the access tube seat and extending upwardly above the surfaceof the water, a ring of deformable material at the lower end of theaccess tube adapted to be deformed against the walls of the channel bythe weight of the access tube to seal the lower end of the access tube,the lower end of the access tube having an enlarged diameter to increasethe force exerted by hydraulic pressure urging the access tube againstthe platform.
 6. A platform for supporting wellheads of offshore wellsbelow the surface of water comprising a plurality of platform legsengaging the ocean floor and extending upwardly therefrom to a level inthe range of 50 to 200 feet below the surface of the water, buoyancytanks secured to the platform legs at the upper end thereof, oil storagetanks supported by the legs at the upper ends thereof, a deck supportedabove the tanks by the platform legs, an access tube base platesupported by the deck, a plurality of guide tubes extending downwardlythrough the access tube base plate and the deck, wellhead structuresconnected to casing extending through the guide tube, an access tubeseat on the access tube base plate encircling the wellhead structuresand opening upwardly to receive an access tube, oil lines extending fromabove the access tube base plate within the access tube seat to the oilstorage tanks, air lines extending from within the accesS tube seatabove the access tube plate to the buoyancy tanks, and outlets in thelower portion of the storage tanks and buoyancy tanks to permit the flowof water into and from such tanks.